The present invention relates to the fabrication of three-dimensional objects using additive process modeling techniques. More particularly, the invention relates to a method for calibrating extrusion tips in a three-dimensional modeling machine.
Additive process modeling machines make three-dimensional models by building up a modeling medium, usually in planar layers, based upon design data provided from a computer aided design (CAD) system. A mathematical description of a physical part to be created is usually split into planar layers, and those layers are individually shaped and applied to produce the final part. Three-dimensional models are used for functions including aesthetic judgments, proofing the mathematical CAD model, forming hard tooling, studying interference and space allocation, and testing functionality. The dominant application of layered manufacturing in recent years has been for rapid prototyping.
Examples of apparatus and methods for making three-dimensional models by depositing solidifiable modeling material are described in Crump U.S. Pat. No. 5,121,329, Batchelder, et al. U.S. Pat. No. 5,303,141, Crump U.S. Pat. No. 5,340,433, Batchelder, et al. U.S. Pat. No. 5,402,351, Crump et al. U.S. Pat. No. 5,503,785, Abrams et al. U.S. Pat. No. 5,587,913, Danforth, et al. U.S. Pat. No. 5,738,817, Batchelder, et al. U.S. Pat. No. 5,764,521 and Comb et al. U.S. Pat. No. 5,939,008, all of which are assigned to Stratasys, Inc., the assignee of the present invention. An extrusion head extrudes solidifiable material in a fluent strand (also termed a “bead” or “road”) from an extrusion tip onto a base. An extrusion head may have several extrusion tips in order to extrude different materials. For example, an extrusion head may have a first extrusion tip that extrudes modeling material to build up a three-dimensional model, and a second extrusion tip that extrudes support material to provide temporary support during a model build cycle. A base comprises a modeling substrate which is removably affixed to a modeling platform. The extruded material is deposited by the extrusion tip layer-by-layer in areas defined from the CAD model, as the extrusion head and the base are moved relative to each other by mechanical means in three dimensions. It is important to maintain a proper distance between the extrusion tip and the base while the model is being built to ensure proper construction of the model. If the extrusion tip is too far away from the base, then the build material may be misplaced or deformed. Conversely, if the extrusion tip is too close to the base, then it may contact the model and cause damage to the model and possibly the extrusion tip or head itself. Furthermore, it is important to tightly control the distance between extrusion tips in a multiple tip system to ensure material layers are properly placed on the substrate or on top of one another.
Once finished, the model is removed from the substrate. A solidifiable material which adheres to the previous layer with an adequate bond upon solidification is used as the modeling material. Thermoplastic materials have been found particularly suitable for these deposition modeling techniques. Other additive process manufacturing techniques include depositing UV curable polymers as in Masters U.S. Pat. No. 5,46,569; jetting of droplets of material as in Helinski U.S. Pat. No. 5,50,515; extruding a settable plastic in vertical strips as in Valavaara U.S. Pat. No. 4,749,347; laser welding deposition as in Pratt U. S. Pat. No. 5,038,014; stacking and adhering planar elements as in DiMatteo U.S. Pat. No. 3,932,923; and applying shaped layers of paper as in Hull U.S. Pat. No. 5,82,559.
Several different types of rapid prototyping machines are commercially available. This commercial availability makes three-dimensional modeling very convenient for consumers because they can create three-dimensional models right at their own facility. However, the machines also require servicing from time to time such as when an extrusion tip may become unusable or unreliable due to a back-up or solidification of modeling material inside the tip. When the flow of modeling material through the extrusion tip is obstructed installation of a new tip is typically necessary. Consumer-replaceable components within the rapid prototyping field have become more available including replacement extrusion tips. While consumer-replaceable extrusion tips have made machine repairs more convenient, it also requires calibration of the tip once it has been replaced or re-installed. The calibration routine includes calibrating a Z-axis tip-to-substrate offset to ensure that the system knows the spatial relationship between the extrusion tip and the substrate prior to building a model. Furthermore, the calibration routine may include calibrating an X-axis and Y-axis tip-to-origin offset to ensure that the system knows the spatial relationship between the extrusion tip and an origin on the substrate. If multiple tips exist, the calibration routine also includes a Z-axis tip-to-tip offset, an X-axis tip-to-tip offset, and a Y-axis tip-to-tip offset. Without calibration, the position of the extrusion tips relative to the base and relative to each other may be incorrect, which may result in the inability of the modeling system to build accurate, error-free models.
Traditionally, calibration routines consisted of a manual or “eyeball” method performed by a trained consumer or technician. Previously, identifying any Z-axis tip-to-tip offset typically involved extruding layers of material and then manually measuring the thickness of the extruded material with a caliper. Similarly, identifying any X-axis or Y-axis tip-to-tip offset typically involved manually measuring the position of the extruded material along the X-Y axis. The tip-to-substrate offset is typically determined by etching a series of consecutive numbers into the substrate at increasing distances between the extrusion tip and the base and “eyeballing” the highest visible number etched into the substrate. The tip-to-origin offset was typically calibrated during assembly or as part of an extrusion head gantry position calibration. Unfortunately, calibration routines involving manual or “eyeball” methods can be unreliable and time-consuming. Additionally, because proper manual calibration requires operator judgment, it can be difficult for inexperienced users to identify the correct calibrated offsets.
Incorrect calibration of extrusion tips can result in the failure to form or build the three-dimensional model. Therefore, there exists a need for an automatic extrusion tip calibration routine that does not require operator intervention or judgment.